Control system



Nov. 9, 1937.

Filed Feb. 25, 1935' H. H. GORRIE 2,098,914

CONTROL SYSTEM 4 Sheets-Sheet l mvENToR HAM/Apo 60m2/f H. H. GORRIECONTROL SYSTEM Nov. 9,A 1937.

Filed Feb. -25, 1955 4 Sheets-Sheet 2 INVENTOR HAM/ARO H Go/P/Q/E BY ofa/A,

ATTOR Y H. H. GoRRn-z CONTROL SYSTEM Nov. 9, 1937.

4 Smets-sheet 3 Filed Feb. 25, 1935 ATTO EY l INVENToR Nov. 9, 193 7.

H. H. GoRRlE 2,098,914

CONTROL. SYSTEM Filed Feb. .25, 1955 4 Sheets-Sheet 4 /f 'i l 4a 4/ 20|Y, /9 /oA I n I -f-d 22 '23 a7 i l 25 43 l 26 M 24 f r 36 43A V33 27 Q.iw;

INVENTOR l' l .v HA/mpo /v Gma/E Patented Nov. 9, 1937 UNITED STATESCONTROL SYSTEM Cleveland Heights, Ohio, as- Meter Company, a corporationHarvard H. Gorrie, signor to Bailey of Delaware Application February 25,1935, Serial No. 8,047

11 Claims.

This invention relates to control systems for establishing ormaintaining substantially constant any desired electrical, thermal,chemical, physical or other variable condition through the control o-f acorrective agent or agents. More particularly my invention relates tocontrol systems wherein a fluid pressure is utilized as the motivepowerI for actuating devices to control the rate of application ofcorrective agents.

It is an object of my invention to provide a control system wherein thecondition under control is rapidly restored to a predetermined value,upon deviation therefrom, without over-travel or hunting.

A further object of my invention is to provide a control system whereinthe control of the pressure fluid by a device sensitive to thecontrolled condition may be readily transferred to manually-operateddevices without setting up disturbances in the system.

A further object is to provide a control system wherein individualunits, each contributing to the production of the controlled conditionmay be operated at different rates, one from another, and wherein thecontrol of the rate of supply of an agent, or agents, by the controlledcondition to each unit is modified to maintain such units at highestoperating eiciency.

These and other objects will be apparent from the following descriptionand the drawings in which:

Fig. 1 is a diagrammatic representation of a control system yembodyingmy invention.

Fig. 2 is a diagrammatic representation of another control systemembodying my invention.

Fig. 3 is a diagrammatic representation of another arrangement to whichthe invention is applied.

Fig. 4 is a sectional elevation of a standardizing or pressure balancingdevice utilized in my invention.

Fig. 5 is a sectional elevation of one type of pilot valve which may beutilized with my invention.

Fig. 6 is a schematic illustration partially in section of a selectorswitch utilized in my invention.

Referring to Fig. 1, I have therein shown my control system utilized tomaintain a predetermined temperature within a tank I, which is suppliedwith a heating agent such as steam through a conduit 2. For regulatingthe ilow of steam to the tank a valve 3 is located in the conduit 2 andactuated by a pressure fluid motor 4. As shown the pressure iluid motor4 is effective for positioning a movable valve member 5 against theprogressively increasing resistance of a spring 6 as the pressure of theuid supplied the motor 4 increases.

Within the tank I may be disposed the bulb 'l of a temperature sensitivedevice having a Bourdon tube 8 adapted to position a movable valvemember 9 of a pilot valve I0 to establish a fluid pressure in accordancewith the temperature within the tank I. This pressure is in turneffective through 'the agency of a standardizing or pressure balancingrelay II for establishing a loading pressure normally governing theactuation of the motor 4. The loading pressure is conducted through apipe I2 to a selector valve I3 wherein it is effective for establishinga control pressure transmitted through the pipe I4 to the motor 4. Thearrangement is such that as the temperature within the tank I increases,the pressure transmitted to the standardizing device II through theagency of the pilot I0 is proportionately decreased, thereby eiecting amovement of the valve member 5 in a closing direction to decrease therate of flow of steam to the tank I.

'Ihe selector valve I3 is provided with suitable manually-operatedvalves and mechanisms whereby control of the motor 4 may readily betransferred from the loading pressure established by the standardizingrelay II to a loading pressure established by an operator or attendant.

In Fig. 5 I have shown in detail the pilot valve I0 which I employ as apart of my control system, and which forms the subject matter of anapplication of Clarence Johnson, Serial N0. 673,212 led in the UnitedStates Patent Oiice May 27, 1933. The movable valve member 9 extendslongitudinally through a passageway I5 and is provided with lands I6positioned adjacent annular outlet ports I1. Fluid pressure is admittedto the passageway I 5 through an inlet port I 8 and is reduced tosubstantially atmospheric pressure in passing the lands I6 which are ofslightly less diameter than that of the passageway I5. Thus a constantilow of pressure fluid exists through the passageway I5 around the landsIB to the atmosphere at each end of casing I0. It is evident thereforethat a pressure gradient exists across each land I6 and the pressureestablished at the outlet ports will depend upon the position of thelands I6 relative to the ports I'I. The ports I1 are of relativelynarrow Width compared to the length of the lands I6, so that if desireda range of pressures at the outlet ports I1 may be established fromsubstantially atmospheric pressure to REISSUED MAY. 2 0 1941 thepressure of the fluid admitted to the passage- Way I5 from the inletport I8. Movement of the memberl9 necessary to produce the desired rangein pressures may be varied by changing the shape of the lands I6. Forexample, if it is desired that thc-complete range in pressures beproduced byva. small movement of the member 9, the lands may be maderelatively short, whereas if it is desired that a considerable motion ofthe member 9 be required they may be elongated and their shape varied togive any desired characteristic between movement of the valve member 9and pressure at the ports Il.

It is to be noted that as the movable valve member 9 is positionedupwardly (Figi 5), the pressure established at the upper outlet port Ilincreases, whereas that established at the lower outlet port Ildecreases. By this arrangement it is possible to obtain a loadingpressure, either varying directly with the magnitude of the crontrolledcondition, or inversely as the magnitude of the controlled condition. Inpractice it is customary to insert a suitable plug in the port not inuse, for example, the control system illustrated in Fig. 1 is arrangedto establish a loading pressure varying inversely as the temperaturewithin the tank I. Therefore, connection from the pilot ill to thepressure balancing relay I I is made to the lower port and a suitableplug inserted in the upper outlet port I'I.

It is an object of the control system disclosed in Fig. 1 to maintainthe temperature within the tank I at some predetermined or desiredmagnitude. One type of control system well known in the art attempts toaccomplish this by positioning the valve 5 in proper sense to restorethe temperature to the predetermined magnitude at a rate proportional tothe amount of deviation of the actual temperature from the desiredtemperature. This type of control, which I have termed floating controlfrequently produces a hunting cycle, particularly if the rate ofresponse of the temperature or other controlled condition to variationsin the rate of supply of the agent producing the controlled condition isdelayed. Thus the rate of supply of steam to the tank I may have beenincreased sumciently to restore the temperature to the desired value,while due to the time delay or lag between the increase in rate andtemperature response, the temperature Within the tank l is still belowthe desired magnitude. Accordingly this type of control will continue toincrease the rate of admission of steam to the tank I, when actually therate of admission has been increased labove that necessary. Accordingly,the temperature .will eventually rise above that desired and the controlsystem operate to decrease therate of supply of steam. However, beforethe temperature is reduced to that desired, the control system will haveoperated to decrease the rateI of admission of steam below thatnecessary to produce the desired temperature, thus causing thetemperature to fall below that desired; the alternate rise and fallcontinuing indenitely, such a cycle being commonly termed a huntingcycle which may or may not be attenuated.

A second type of control commonly employed is known as positioningcontrol wherein for every value of the controlled condition there ismaintained a certain rate of application of the agent, or agents,producing that condition. For example, in the embodiment disclosed inFig. 1 this type of control would upon a decrease in temperature withinthe tank l of a certain amount oper- 2,098,914 -ate to open the valve 3a predetermined amount,

exhausted through a port 29.

thus increasing the rate of admission o! steam to the tank. This type ofcontrol may be readily adjusted so that no appreciable over-shooting orhunting occurs. As readily apparent, however, It does not maintain thecontrolled condition at an exact predetermined or desired magnitude, butmerely maintains it within a predetermined range of values, and for thisreason is frequently objectionable. In my invention I have combined thesalient features of both systems and have produced a control systeminherently stable in that there is no tendency to set up a hunting cycleor to over-shoot, and at the same time maintaining the controlledcondition at the predetermined or desired magnitude. I have accomplishedthis desired result by combining the two systems, and have devised whatI conveniently term a positioning-floating control. Upon a deviation ofthe controlled condition from the desired magnitude my improved controlsystem iirst operates to vary the rate of application of the agent, oragents, producing the condition a proportional amount, and thereafter toslowly vary the rate of application of the agent, or agents, until thecondition is restored to the desired magnitude. Basically the controlsystem operates to rst give a response proportional to the rate ofchange in magnitude of the condition being controlled, and thereafter togive a continuing response initially proportional to the amount ofdeviation of the controlled condition from the desired magnitude. Bythus -combining the two systems the range of the positioning control maybe suiciently great so` that the rate of application of the agent, oragents, is varied only sufciently to materially retard or stop a furtherdeviation of the controlled condition from the desired value. Thereafterthe oating control continuously tends to effect a further variation inthe rate of application of the agent, or agents, until the controlledcondition is restored to the desired magnitude. However, as thecontrolled condition is returningk toward the desired magnitude thepositioning control effects a corrective action in a sense tending toprevent the return of the controlled condition to the desired magnitude;the oating control does not produce a hunting cycle, but the approach tothe desired magnitude is made asymptotically.

In the control system shown in Fig. 1 the standardizing or pressurebalancing relay II sensitive to the pressures established by the pilotI0 establishes a loading pressure governing the actuation of the motor 4in accordance with the principles briefly described. Referring now toFig. 4 the pressures established by the pilot valve I0 are admittedthrough a port I9 to a chamber 20, one side of which comprises aflexible wall or diaphragm 2l. The diaphragm 2| also-forms one side of achamber 22, which may or may not be open to the atmosphere through aport 23, depending upon the use to which the device may be put, ashereinafter more fully explained. The

diaphragm 2l is connected to a diaphragm 24 by suitable mechanical meansshown as a movable member 25. The diaphragm 24 forms a bleed chamber 26and a control chamber 21. Pressure iiuid from a suitable source may beadmitted to the chamber 2l through a port 28 and may be Movable ballvalve members 30 and 3i normally urged against the ports 23 and 29respectively, by springs 32 are adapted to control the passage ofpressure fluid to and from the chamber 2l.

So `that the pressure within the chamber 20 necessary to maintain themovable member 25 in the neutral position may be varied as desired, acompression spring 39 anda tension spring 40 are shown located withinthe chamber 20. The compression spring 39 is arranged to produce adownwardly acting force upon the member 25, whereas the tension spring40 is arranged to produce an upwardly acting force on the member 25. Thetension spring 40 is shown secured to a longitudinally movable block 4|.A manually adjustable means comprising a screw 42 threaded into theblock 4| provides a means for positioning the block 4| to vary theeffective force of the tension spring 40 upon the member 25, andcorrespondingly vary the value of the pressure in the chamber 20 whichwill maintain diaphragm 2| and member 25 in neutral position.

Disposed within the chamber 21 and fulcrumed intermediate the valvemembers 30 and 3| is a beam 33 carrying depending extensions 34, adaptedto engage the valve members 30 or 3| upon angular displacement of thebeam 33 from the horizontal or neutral position. The beam 33 is urged bya spring 35 against the member 25, downward movement of which causes thebeam 33 to be positioned in a counter-clockwise direction, forcing thevalve member 30 away from the port 28 and-admitting pressure fluid tothe chamber 21. Conversely, upward movement of the member 25 causes thebeam 33 to be positioned by spring 35 in a clockwise direction forcingthe valve member 3| from the port 29 and exhausting pressure iluid fromwithin the chamber 21.

The bleed chamber 26 is shown in communication with the. control chamber21 through a pipe 36 and a throttling valve 31 provided with anadjustable valve member 38 for varying the resistance to the passage ofpressure fluid between the chambers. With the valve member 38 in aposition to completely prohibit passage of pressure fluid, an increasein pressure within the chamber 20 will increase the force actingdownwardly upon the diaphragm 2| thus producing a downward motion of themember 25 effecting an opening of the port 28, permitting pressure fluidt0 be admitted to the chamber 21 until the increasing pressure thereinacting upwardly is sufficient to balance the increase of pressure withinthe chamber 20 when the member 25 will return to the neutral positionand valve members 30 and 3| will completely close the ports 28 and 29respectively. Conversely upon a decrease of pressure within the chamber20 the member 25 will move upwardly, opening the exhaust valve 3|, andallowing pressure fluid within the chamber 21 to exhaust until thepressure therein balances that within the chamber 20, when themember 25will be restored to the neutral position. So far, the action exemplifieswhat I have termed positioning control.

With the adjustable valve member 38 open so that pressures existingwithin the chambers 26 and 21 immediately equalize, upon the member 25being moved downwardly from the neutral position by an increase inpressure within the chamber 20 the valve member 30 will remain openuntil the pressure Within the chamber 20 is restored to the originalvalue, as the pressure existing within the chamber 21 would merelycounter-balance the pressure in the bleed chamber 26. 'Ihus the soleforce acting upon the movable member 25 would be that due to thepressure in chamber 20 against the diaphragm 2|. 'I'his would result inwhat I have termed floating control.

If the throttling valve member 38 is moved to a nearly closed positionso that the flow of pressure fluid between the chambers 26 and 21 is 5materially restricted, then upon a change of pressure within the chamber20 from the predetermined value either the valve member 30 or 3| will bemoved from its seat, but due to the restricted passageway between thechambers 25 10 and 21 a change in pressure within the chamber 21 willnot immediately eiect an equal change in the pressure within the bleedchamber 26 and -will accordingly produce a force upon the movable member25 counter-balancing the force pro- 15 duced by the change in pressurewithin the chamber 20. When, therefore, the change in pressure Withinthe chamber 21 is proportional to the change in pressure within thechamber 20, the

member 25 will be restored to its neutral position 20 and a furtherimmediate change of pressure within the chamber 21 will not take place.As, however, there is now a pressure diierential existing betweenr thechambers 26 and 21, a seepage of pressure fluid will take place, thuspartially neu- 25 tralizing or counterbalancing the force produced bythe pressure within the chamber 21, effective for maintaining the member25 in a neutral position. The member.25 will be moved from the neutralposition, allowing a further change o1' 30* pressure within the chamber21, which will cause the seepage of pressure between the chambers 26 and21 to continue. The pressure within the chamber 21 will accordingly becontinuously modified after an initial change due to departure of 35 thepressure within the chamber 20 from the predetermined value. The resultis a combination iloating-positioning control,l as previously explained.

Appreciating that the principle of operation of 40 a device isfrequently more readily understood by reference to specific examples, itmay be assumed that the tension of the spring 40 is adjusted so that themember 25 is in the neutral position with a pressure of 18 lb. persquare inch existing within 45 the chamber 20, and with equal pressuresexisting within the chambers 26 and 21 and 22 open to atmosphere. Assumenow that the pressure within the chamber 20 is increased to 19 poundsper square inch. Immediately the member 25 will 50 be positioned in adownward direction, moving the valve member 30 from the port 28 andaclmitting pressure fluid to the chamber 21 until the pressure thereinincreases one pound per square inch when the force acting upwardly on 55the chamber 21- to the chamber 26, decreasing the 65 net force actingupwardly against the diaphragm 24, destroying the state of equilibriumand again producing a downward positioning of the member 25 and openingthe valve 30. It will be appreciated that actually the operation iscontinuous, the pressure within the chamber 21 gradually increasing at arate dependent upon the differential in pressure existing between thechambers 26 and 21. It is to be further noted that once a differentialpressure is established between the chambers 75 26 and 21, thatdinerential will be substantially maintained 'until there is a furtherchange in pressure within the chamber 20. For example, assuming that thepressure within the chamber 20 further increases from 19 pounds persquare inch to 20 pounds per square inch, the member 25 wouldimmediately be positioned downwardly until there was a proportionateincrease in pressure within the chamber 21. A differential pressure oftwo pounds per square inch would now exist between the chambers 26 and21, and the seepage of pressure viluid would progress at substantiallythe square of the rate, so that the pressure existing within the chamber21 would increase at twice the rate compared to the rate of increasewhen one pound differential existed between the chambers 26 and 21.pressure within the chamber 20 should decrease to 19 pounds per squareinch, an immediate upward positioning of the member 25 would takeV placemoving the valve member 3| from the port 29, and lowing pressure fluidto exhaust from the chaincer 21, until the net upward force acting uponthe diaphragm 24 had been decreased by one pound per square inch whenthe member 25 would again be positioned to the neutral position andvalve members 30 and 3l would both be in the closed position. However,the pressure existing Within the chamber 21 would still be substantiallyone pound greater than that existing in the chamber 26, thus permittinga seepage of pressure between the two chambersV and, in the mannerhereinbefore described, to 'produce a continuously increasing pressurewithin the chamber 21. Assuming now that the pressure within the chamber20 should decrease to the neutral pressure of 18 pounds per square inch,the valve member 3l would be opened until no diierential existed across'the diaphragm 24 effective for producing a force on the member 25,when'the member 25 would be positioned to the neutral position.

The chamber 21 'is provided with aA port 43A which may communicate withsuitable responsive devices for governing either directly or indirectlythe application of an agent effecting or producing the controlledcondition. In Fig. 1 for example, I have shown the pressure establishedwithin the chamber 21 in communication through the pipe l2 with aselector valve i3 for governing the pressure fluid effective within thevmotor 4. The pressure established by the pilot ill, in accordance withthe temperature within the tank i, is transmitted to the chamber 20 andis effective for producing a loading pressure within the chamber 21varying in accordance with v changes in the temperature within the tankl,

and inaccordance with the deviation of the temperature from the desiredvalue. In operation the tension of the spring 4D may initially be soadjusted that with the throttling valve member 38 open, allowingpressures to equalize instantaneously between chambers 26 and 21, themember 25 will be in the neutral position when the pressure within thechamber 2li is that esestablished by the desired temperature within thetank i. The throttling valve member 38 may then be so adjusted as toprovide a desired rate of bleed between the chambers 26 and 21. Toprevent over-travel or hunting, the member 38 may be so adjusted thatafter the initial change in the rate of supply of heating fluid producedby a change in pressure within the chamber 29, the rate at which the owof heating iluid to the If now. the

tank l is varied is slower than, or lags, the responsiveness of thetemperature within the tank vi to changes in the rate of supply ofheating rective agent substantially in unison with and in sensedependent upon changes in the magnitude of the controlled condition andthereafter occasions a continuing secondary change substantiallyproportional to the amount of and in sense dependent upon the deviationof the controlledcondition ,from the desired magnitude; or in otherwords a control of relatively high sensitivity but low speed issuperimposed upon a control of low sensitivity but high speed.

It 'is desirable in some applications ot automatic control systems thatthe valve or other means of regulating the corrective agent bepositioned directly in accordance with variations in the pressureestablished by the pilot valve r other means sensitive to changes in thecontrolled condition. Referring to Fig. 1 it may be desirable forexample that the pilot valve l0 be arranged to produce an increasingpressure effective upon the standardizing relay Il with increasingtemperatures within the tank I. The standardizing relay may readily bearranged for proper actuation of the valve by introducing the pressurefrom the pilot I0 into the chamber 22 through the port 23, permittingthe chamber 20 to remain open to the atmosphere. Under such anarrangement, upon the pressure from the pilot valve l ll increasing, dueto an increase in the controlled condition above the desired value. theloading pressure within the chamber 21 will in unison therewith bereduced a proportionate amount and thereafter will continue to bereduced substantially in proportion to the amount the pressure withinthe chamber 22 is above the value corresponding to the desired magnitudeof the condition.

In the embodiment of the standardizing relay illustrated in Fig. 4, thearea of the diaphragm 24 upon which the pressure fluid within thechamber 26 is effective is less than the area of the diaphragm 24 uponwhich the pressure uid within the chamber 21 is effective. For, asshown, the chamber 22 is pressure sealed from the chamber 26 by asuitable expansible contractible bellows 43, which reduces the effectivearea of the upper side of the diaphragm 24. Accordingly, therefore, foreach pressure within the chamber 20 the movable member 25 will berestored to the neutral position when the pressure within the chambers26 and 21 are equal and of a certain value.

L ''his may be shown mathematically as follows:

P0=Pressure within chamber 2o corresponding to the desired value of thecontrolled condition.

P1=Actual pressure within chamber 2li.

P2=Actual pressure within chamber 22.

P3=Actual pressure within chamber 26.

P4=Actual pressure withinchamber 21.

Ai--Area upon which pressure P1 is effective.

A2=Area upon which pressure P2 is effective.

A3=Area upon which pressure P3 is effective.

.A4-:Area upon which pressure P4 is effective.

S=Initial spring force.

Cil

Cir

Then when member 25 is in the neutral position: PiA1-P2A2+P3A 3-P4A4-S=O(1) But by construction:

P2Az=K1=A constant S :K z :A constant And when in equilibrium:

Then from (3) Which reduces to:

Kx Poa (5) Therefore:

P! =P4(1 )+Poa (6) 0r:

P1A1 P041- 'I'hus for each value of P1 there exists a certain value ofP4 at which the member 25 will be in the neutral position. For a givenvalue of P1 the corresponding neutral value of P4 increases as (A1-A3),which is the area of the expansible contractible bellows 43, decreases;and when (A1-A3) is O then for each value of P1, P4 will have a neutralvalue of innity.

In general it is apparent therefore that the standardizing relay H asshown in Fig. 4 operates to produce an initial response in proportion toand in unison with changes in the controlled condition; and thereafterto produce a delayed response initially proportional to the amount ofdeviation of the controlled condition from the desired value, andcontinuing until a predetermined relation exists between the loadingpressure within the chamber 20 and the controlling pressures within thechambers 26 and 21. Or in general it may be said to superimpose asecondary slow speed positioning control of relatively high sensitivityupon a primary high speed positioning control of relatively lowsensitivity. It is apparent that by varying the effective area uponwhich the pressure within the chamber 25 is effective, which may readilybe accomplished by varying the diameter of the bellows 43, any relationdesired may be obtained between the primary and secondary controls.

The condition hereinbefore mentioned when (A1-A3) equals O, and no valueVof P4 other than infinity satisfies the equation of equilibrium, may beobtained by introducing the loading pressure (P1) into the chamber 26,and connecting the pipe 36 and throttling valve 31 to the chamber 20.Thus as the eiiective area of the diaphragm 2| is equal to the effectivearea of the diaphragm 24 upon which the controlling iiuid pressurewithin i the chamber 21 is eiective, (A1-As) equals O, and upon adeviation of the controlled condition from the desired value the rate ofapplication of the corrective agent will be varied until the controlledcondition is restored to the desired value or until the regulator of thecorrective agent reaches an extreme of travel. It is apparent that therelative areas of the diaphragms 2| and 24 may be varied as desired sothat the secondary response may bear any desired relation to the primaryresponse, or so that the change in loading pressure produced in thecontrol chamber 21 for a given change in pressure within the chamber 20,or 22, may be varied as desired.

In Fig. 1 I have shown the controlling fluid pressure conducted from thestandardizing or pressure balancing relay Il through a pipe l2 to aselector switch I3, which provides a convenient means for readilytransferring control of the motor 4 either partially or entirely fromthe controlled condition to manual control. In Fig. 6 I haveschematically illustrated the selector valve I3 provided with a suitablemounting plate 44, readily fastened to a panel or other mounting means.Journaled in the mounting plate 44 and extending rearwardly therefrom isa cam shaft 45, to which is secured a hand operable-valve switch 46.Suitably arranged on the cam shaft are cams 41, 48 and 49 forpositioning the movable valves 50, 5| and 52 of valve bodies 53, 54 andrespectively. On the mounting plate 44 may be inscribed suitable legendsfor indicating the existing status of the control system and directionsfor transferring the control from automatic to hand, or vice versa. Asshown, the valve switch 46 is in the hand" position, indicating that thevalves 50, 5| and 52 are positioned s`o that the controlling pressuretransmitted to the valve 3 may be varied manually entirely independentof the loading pressure produced by the standardizing relay Il byangularly positioning a knob 56. As indicated by the legend angularpositioning of the knob 56 in a clockwise direction decreases thecontrolling pressure whereas counter-clockwise positioning increases thecontrolling pressure.

Manual positioning of the knob 56 serves to actuate a relay 58, which inmany aspects is similar to the standardizing or pressure-balancing relayII hereinbefore described. The knob 56 is secured to a shaft 51journaled in the mounting plate 44,-and passes through the wall of therelay 58. The relay 58 is divided into two chambers 20A and 21A by adiaphragm 59. Positioned in the chamber 20A is a compression spring 39Aurging the diaphragm 59 in one direction. Likewise positioned in thechamber 20A is a tension spring 40A fastened to the diaphragm 59 and toa longitudin-ally movable block 4IA, and urging the diaphragm 59 in theopposite direction. The movable block 41A is threaded to the shaft 51and upon angular positioning of the shaft 51 is moved longitudinally inthe chamber 20A, thus increasing or decreasing the tension of the spring40A. When the knob 56 is angularly positioned in a clockwise directionthe movable block 4 IA is moved to the right, as viewed in the drawings,thus increasing the tension of the spring 40A, and reducing the netforce of the springs 39A and 40A against the diaphragm 59.

Located in the chamber 21A is a fulcrumed beam 33A adapted to actuate apressure fluid inlet valve 30A when displaced from the neutral positionin a counter-clockwise direction, or to actuate a pressure fluid exhaustvalve l A when displaced from the neutral position in a clockwisedirection. Pressure fluid admitted to the chamber 2HA is effective formaintaining the diaphragm 55 in a neutral position and is transmittedthrough the valve 55 to the pipe l5 for actuating the motor ll.

The movable valve member 55 controlling the ingress of iiuid pressurefrom the pipe l2 to the chamber 25A is shown in the closed position,whereas the movable valve member 5l permitting egress of the pressureiluid within the chamber 25A to the atmosphere, is open. Accordingly theforce urging the diaphragm 55 to the left, as viewed in Fig. 6, is thatproduced by the springs and 55A. If for example it is desired to reducethe uid pressure effective on the motor d, the hand operable knob 55 isrotated in a clockwise direction, thus increasing the tension of thespring 55A, but reducing the net force urging the diaphragm 55 to theleft. Accordingly the pressure necessary to produce an equal butopposite force to maintain the fulcrumed beam 53A in the neutralposition is reduced, and the fulcrum beam A is displaced clockwise.actuating the valve member SMA allowing the pressure within the chamber25A to decrease until it is in proportion to the force produced by thesprings 55A, 635A. Further displacement of the knob 55 eects a furtherdecrease in fluid pressure necessary to maintain the diaphragm 55 in theneutral position, and the relay 55 provides a convenientmanually-operable means for varying the fluid pressure eective upon themotor il through any range desired.

In order that the operator may be advised of the position of the valve 5at all times, a pressure gage 55 may be provided, which is connected tothe chamber ETA. As the valve 5 is positioned in accordance with thepressure uid transmitted to the motor l from the chamber 21A anindication of such pressure is in reality an indication of the positionof valve 5, and the gage 55 may if desired be graduated to indicatevalve position.

An operator thus manually adjusting the control system is continuouslyand instantaneously advised of changes in the rate of application of thecorrective agent. 1

When it is desired to transfer the means regu- .lating the rate ofapplication of the corrective agent from hand to automatic control, thetransfer switch t6 is rotated 90 in the direction indicated by the arrowto the reset" position. Such rotation eifects an opening of the valve55, and a closure of the valves 54 and 55. Pressure variations from thestandardizing relay ll are thus transmitted through the pipe l2 to tlnechamber 25A and are effective upon the diaphragm 59.` The magnitude ofthe pressure within the pipe i2 is indicated by a gage 5l. An operatormay then observe the difference between the loading pressure produced bythe standardizing relay ll and that which will be made effective uponthe motor di by determining t-he difference between the readings of thegages 6i] and 5l. In order that the transfer from hand to automaticcontrol may be made as smoothly as possible without causing disturbancesin the system it-is desirable that the diierence in the loading pressuretransmitted through the pipe l2 and that which will be made effectiveupon the motor t through the pipe lll, be as small as possible beforethe transfer is made. Thus with the transfer switch in the resetposition an operator is given an opportunity to determine thisdifference,

accepta and proper manipulation of the knob 56 may make the pressuresidentical before making the transfer.

lliurther displacement of the transfer switch 55 from the reset positionto the automatic position permits the `valve 55 to remain open, thevalve 55 to remain closed, but opens the Valve 55, thus permittingpressures within the chamber NA to be transmitted through the pipe l5 tothe motor t and variations in loading pressure conducted through thepipe l2 to the chamber 25A will thereafter produce correspondingvariations in the controlling pressure transmitted to the motor 5. Ifdesired the controlling pressure transmitted to the motor t, may beincreased above or decreased below the loading pressure established inthe chamber 25A by manual operation of the knob 55, which thus providesa means for modifying the control of the rate of application of theproducing agent by the controlled condition to compensate or correct,for example, for variations in the thermal content, chemicalconstituentspetc., of the producing agent.

In transferring from automatic to hand control it is also desirable thatthe operation be accomplished without undue disturbance in the controlsystem or in the apparatus to which it is applied. To accomplish this areset position is provided as shown between the automatic and handpositions. is closed, Valve 5ft is' opened, allowing the pressure uidwithin the chamber 25A to exhaust;

and valve 53 is closed. The knob 55 may then be.

prior to the transfer switch being moved from-y the automatic positionto the reset position; and as the'valve 55 is closed such adjustment maybe made without disturbing the position of the valve 5. After thecontrolling fluid pressure has been brought to the desired value bymanipulation of the knob 55, the transfer switch may be turned to theHand position, with the as` surance that the valve 5 will not bepositioned suddenly from its former position.

In Fig. 2 I have shown instrumentalities in which my invention isembodied, utilized to control the flow of feed water to a boiler. Such acontrol system may be of the S-elvement type wherein the ow of feedWater is regulated in accordance with the three elements-steam ow fromthe boiler, feed Water to the boiler, and water level in the boilerdrum. In the drawings a valve 53 is positioned in a pipe 64 for thecontrol of feed Water to the steam and water drum 55 of a boiler (notshown), and a conduit 56 is provided for transmittal of steam from thedrum 55 to a point of usage (not shown). The rate of steam flow throughthe conduit 66 is measured by a suitable ow meter 5l which may be of thetype disclosed in Patent 1,123,164 to Bailey. The flow meter 6l isprovided with an arm 68 angularly positioned in accordance with the rateof ow of steam through the conduit 66, andv adapted to position a pilotvalve 69, similar to that shown in Fig. 5, to establish a uid pressurevarying in direct proportion to changes in the Avided between chambers18 and 19 corresponding respectively to chambers 26 and 21 of relay Il.The chamber 18 being open to the atmosphere through the throttling valve80, the pressure balancing relay 15 will operate to establish a loadingpressure within the chamber 19 proportional to the differential inpressures admitted to the chambers 14 and 11. The magnitude of thepressure maintained in chamber 19 for a given differential betweenchambers 14 and 11 may be brought to any desired value by the manuallyadjustable screw 8| effective for varying the net force of the springsacting upon the movable member 84. In operation, upon an increase in.the loading pressure within the chamber 14, due

.within the chamber19 balances the increase in l pressure in the chamber14, when the movable member 84 will be restored to the neutral position.Conversely upon an increase in the rate of flow of feed Water throughthe pipe 64, the

-pressure within the chamber 11 will increase,

causing the movable member 84 to move upward and allowing pressure fluidto exhaust from the chamber 19 until the decrease in pressure within thechamber 19 is equal to or proportional .to the increase in pressurewithin the chamber 11, when the movable member 84 will return to theneutral position. Ifthe pressures within the chambers 14 and 11 increaseor decrease in unison, there will be no change in the force acting uponthe movable member 84 and the presthe pressures established within thechambers 14 and 11 are proportional to the rates of steam ow through theconduit 66 and the rate of flow of feed water through the pipe 64,variations in pressure within the chamber 19 are inferentially vameasure of the difference in rate of feed water to the boiler and rateof steam flow from the boiler. When the rate of flow of feed waterthrough the pipe 64 is equal to or in desired proportion to the rate offlow of steam through the conduit 66, the pressure within the chamber 19will be at some predetermined magnitude as established by the adjustmentof the screw 8l. Upon an increase in the rate of ow of steam ow abovethe rate of ow of feed water, the pressure within the chamber 19 willincrease in proportion to the difference in rate. Correspondingly shouldthe rate of flow of steam decrease below the raterof flow of feed Water,the pressure within the chamber 19 will decrease proportionately.

In the control system shown vin Fig. 2, I preferably utilize thepressure established Within the chamber 19 as an indication of the ratiobetween the rate of flow of feed water to the boiler and rate of 110W ofsteam flow from the boiler and then control the rate of flow of feedWater to the boiler through the agency of the valve 63 to maintain thesaid ratio at a predetermined value, such as unity. In producing a fluidpressure for regulating the positioning of the valve 63, use may be madeof a standardizing'relay such as shown in Fig. 4. In Fig. 2 the pressurewithin the chamber 19 is transmitted through a pipe 84A to the chamber20 of the standardizing relay Il. cordingly upon a deviation of pressurewithin the chamber 20 from a predetermined value the load- :lng pressurewithin the chamber 21 will first vary proportionately, and thereaftercontinue to vary until the pressure within the chamber 20 is restored tothe desired Value. The loading pressure established within the chamber21 is transmitted to the selector valve I3 through the pipe 85 and thecontrolling pressure established by the loading pressure, and as may bemodified by manual positioning of the knob 56 is conducted through apipe 86 to the motor 81 for positioning the valve 63 In operation,assuming the system to be in equilibrium, that is that the rate of flowof steam through the conduit 66 is equal to or in desired proportion tothe rate of flow of feed water through the pipe 64, that upon anincrease in the rate of flow of steam through the conduit 66, thepressure within the chamber 14 will increase, producing a proportionateincrease in the pressure within the chamber 19. The pressure establishedWithin the chamber 19 will be effective within the chamber 20 of thestandardizing relay Il for producing an initial increase in loadingpressure within the chamber 21, and thereafter to produce a continuousincrease in loading pressure within the chamber 21. The loading pressureestablished within the chamber 21 will be effective through the agencyof the selector valve I I 3 for increasing the pressure fluid effectivewithin the motor 81, thus positioning the valve 63 in an v openingdirection, increasing the rate of flow of feed water through the pipe64. The pressure fluid effective within the motor 81 will continue toincrease due to the continuing increase in pressure within the chamber21 until the rate of flow of feed Water through the pipe 64 is againequal to or in desired proportion to the rate of steam flow through theconduit 66. When this latter condition obtains, the loading pressurewithin the chamber 21 will remain constant until there is a furtherchange in the pressure established within the chamber 19, due to adeviation from the predetermined ratio between the pressures within thechambers 14 and 11.

While the system so far described will maintain the rate of flow of feedwater to the boiler equal to or in desired proportion to the rate offlow of steam from the boiler, it is necessary in order to maintain thewater level within the boiler drum within certain limits to modify thecontrol of rate of flow of feed water by rate of flow of steam inaccordance with variations in the water level. Such modification mayoperate to maintain a constant water level within the boiler variationsin the water level by establishing a` pressure varying in accordancewith water level. The apparatus provided comprises a mercury floatactuated boiler water level indicator 88, having an arm 89 angularlypositioned in accordance with variations in water level` The pilot valve90 is positioned by the arm 89 and establishes a pressure proportionalto the water level, which is transmitted to the chamber 22 of the deviceIl Upon a decrease in water through a pipe 9|.

level the fluid pressure established by the pilot Sil will decrease,effecting a downward positioning of the movable member 25 of the relay li to effect an increase of pressure within the chamber 2l, effectivethrough the selector valve i3 for establishing a controlling pressure inthe motor itl for opening the Valve 63 to increase the rate of flow offeed water through the pipe tl, thus producing an increase in waterlevel. Conversely upon an increase in water level the fluid pressureestablished by the pilot Si@ will increase, effecting an upwardpositioning of the movable member 25, decreasing the pressure within thechamber 2l and correspondingly producing` a positioning of the valve 53to decrease the rate of flow of feed Water to the pipe til, which willproduce a lower water level. l

The selector valve i3 may be used as hereinbefore described to transferthe operation of the valve 63 from automatic to hand control, or tomodify the control of the valve 63 by the loading pressure establishedin the chamber 2l! as may be desired to compensate for temporaryconditions, inaccuracy in the system, etc,

Certain features of the control system disclosed by Fig. 2 and thedescription relating thereto, but not claimed herein, form the subjectmatter of a co-pending application for Letters Patent of the UnitedStates filed concurrently herewith by Paul S. Dickey, Serial #8,023', towhich reference may be had for a more detailed description.

In Fig. 3 I have shown a control system embodying my invention appliedAto the regulation..

of a vapor generating plant. In the drawings a plurality of vaporgenerators, 92, 93 and sil, are arranged to discharge steam into acommon header 95 through steam pipes 96. The rate of fuel supply to eachboiler is controlled by a valve gli, positioned in a fuel supply lineQt. combustion is admitted to the furnace through a duct 99, in which ispositioned a damper it@ for controlling the rate of air supply. Theproducts of combustion are withdrawn through a stack fill, in which ispositioned a damper ft2 for controlling the rate of discharge of theproducts of combustion from the generator.

The control system as illustrated operates to maintain a rate ofcombustion sufcient to supply the varying demands of steam, as indicatedby changes in the steam pressure, and further to control the ratio ofair to fuel supplied each boiler tomaintain operation of the plant atmaximum efficiency. A Bourdon tube 903 is arranged to indicate thepressure of the steam in cooperation with a scale it, and also toposition a pilot valve 1105 for establishing a. fluid pressure varyinginversely as the pressure of the steam Within the conduit 95. Suchpressure is transmitted to the standardizing relay Il, which operates ina manner hereinbefore described to establish a loading pressureeffective for controlling the rate of supply of fuel and air to all ofthe boilers in unison. This loading pressure is preferably relayedthrough a selector valve i3, so that the entire plant may be readilytransferred from automatic to hand control, or the automatic controlmodified to suit temporary conditions. 'Ihe instrumentalities comprisingthe Bourdon tube H13, pilot 05, standardizing relay i l, and selectorswitch i3, may be termed a master control inasmuch as they function toeffect the operation of all of the boilers in unison, and furthermoreare devoted to the maintenance of a predetermined pressure, as for upona deviation of pressure from the desired magnitude a pressure will beestabi Air for of flow of steam from each of the boilers.

lished by the pilot Q05 effective through the agency of thestandardizing relay il for producing a loading pressure instantaneouslyvarying in accordance with the deviation of pressure from acts to givean immediate corrective action pro-1 portional to the rate of change inpressure and thereafter to give a continuing corrective actionproportional to the amount of deviation of the pressure from the desiredvalue.

The loading pressure established by the standardizing relay l l, asrelayed through the selector switch i3, is conducted to boilers 92, 93and gli, through a pipe ft, and is .adapted to control the actuation ofa fluid pressure motor l'l positioning the damper H12 and of the fuelsupply valve QI. Thus upon a decrease of vapor pressure within theconduit 95 the loading pressure established by the standardizing relay ll will increase in unison therewith, effecting a positioning of the fuelsupply valve @l and the damper mit to increase the rate of fuel supplyand air supply to each boiler in parallel. Thereafter the loadingpressure will continue to increase inv proportion to the amount ofdeviation of the steam pressure below the desired value, and effect afurther continuing positioning of the fuel supply valve @l and damperlut to effect a further increase in the rate of fuel and air supply toeach boiler until the steam pressure is restored to the desired value.

The loading pressure established by the standardizing relay l leffective for positioning the fuel supply valve 9i is preferably relayedthrough a` selector valve 53A, so that the rate of fuel supply to eachboiler may be readily transferred from automatic to hand control, or thecontrol of fuel modified in accordance with local boiler conditions. Aswell understood in the art it is frequently desirable that one or moreboilers be maintained at a. constant rate of steaming, and thevariations in load compensated for by varying the ratings' on theremaining boilers. The provision of the individual selector valves ISAin the lines to the fuel supply Valves @l provides a means for readilymaintaining any boiler at a predetermined rate of vapor generation. Itis also frequently desirable that While several of the boilers vary inrating in accordance with variations in vapor usage, that some of theboilers be operated at a proportionately higher rating than the others.The selector valve provides a means for readily modifying the control offuel to provide for this arrangement.

As well known, the ratio between fuel and air supply to the boiler mustbe maintained at a pre--l determined value for maximum operatingeiliciency. To furnish air in excess of the amount dictated by thisratio, or to supply it in less amount, results in a decrease inefficiency. Accordingly, an automatic control system after an adjustmentof the fuel and air to satisfy a change in requirements for steamproduction, should readjust the supply of air if the ratio between fueland air-deviates from the value giving maximum emciency. In the drawingsI have shown a combustion control system, accomplishing this through theagency of my improved control devices. At |108 I have shown a meter ofthe rate The meter m8 is provided with an indicator ille, which incooperation with a scale li will indicate the rate of flow of steam fromthe boiler. The indicator IUS is adapted to move downward upon anincrease in the rate of ilow of steam from the boiler. A similar meterIII is provided with an indicating arm II2 adapted to cooperate with ascale I I 3 to measure the rate of the flow of products of combustionthrough the boiler. The indicating arm I I2 is adapted to move upward asthe rateof iiow of products of combustion increases. The rate of fio-wof products of combustion is inherently an indication of the rate of airsupplied to the boiler and the rate of flow of steam ow from the boileris a measure of the heat supplied by the fuel. Accordingly apredetermined ratio should be maintained between the rate of flow of theproducts of combustion and the rate of flow of steam flow from theboiler for maximum combustion. Such a relation gage as I have hereindescribed and shown more or less diagrammatically may be of the typeshown and described in Patent #1,257,955 to Bailey.

The meters I8 and I I I are adapted to position a pilot valve IN througha suitable differential linkage to establish a. loading pressure inaccordance with the ratio between the rate of flow of steam from theboiler and rate of flow of prodn ucts of combustion through the boiler.In order that the rate of flow of air through the boiler may be variedin response to variations in vapor pressure, and also modified tomaintain a predetermined relation between the fuel supply and airsupply, I have found it advantageous to utilize the pressure averagingrelay 'I5 to produce a loading pressure varying in accordance with thesum of the loading pressures established in accordance vrwith themagnitude of the steam pressure, and the loading pressure established inaccordance with the ratio between fuel flow and air iiow. As in thisparticular instance I desire to add the two pressures, rather than toproduce a loading pressure varying as the diiierence, I connect thepilot valve I I4 to the-chamber 'I8 and the loading pressure from themaster standardizing relay II to the chamber 14. The pressureestablished in the chamber 19 will therefore vary in accordance with thesum of the two` pressures. This pressure is transmitted to a selectorvalve I3B and thence relayed to the fluid pressure motor |01. Thearrangement is such that upon a decrease in pressure the loadingpressure established by the master standardizing relay I I will increaseeffecting a positioning of the damper |02 in an opening direction.Likewise an increase in steam flow with no corresponding increase in airilow will cause the loading pressure transmitted from the pilot II4 toincrease, thus also serving to position the damper I 02 in an openingdirection. The pressures effective for positioning the motor IUT arepreferably relayed through a selector valve ISB so that the control ofair flow through the boiler may be readily transferred from automatic tohand control, or vice versa. 'I'he selector valve I3B also makesprovision for modifying the control of air flow by steam pressure andthe ratio of steam flowair flow.

To maintain a predetermined furnace draft within the boiler furnace Ihave provided a meter II5 having an indicating arm IIS positioned inaccordance with variations in furnace draft. The pilot valve I I'I ispositioned by the indicating arm and establishes a loading pressurevarying directly with furnace draft. Upon an increase in furnace draftfor example, the indicating arm I I6 will move downwardly as viewed inthe drawings, increasing the loading pressure in a pipe I I8,

connected to the selector valve I3C. The loading pressure so produced isrelayed through the selector valve I 3C to a iluid pressure damperoperator IIS. Upon an increase in furnace draft the indicating arm I I6will be positioned downwardly as viewed in the drawings, increasing theloading pressure controlling the positioning of the valve operator II9,which will position the damper |00 in a direction to increase the rateof flow of air to the furnace, thus restoring the furnace draft to thepredetermined value.

While in the foregoing description I have used specific apparatus toillustrate the operation of my invention and have in cases resorted tocertain specic values to more clearly1 explain the principle of myinvention, it is to be understood that I am not to be limited thereby,but that my invention is applicable to wide variety of apm plications.

Certain features of my invention disclosed but not claimed herein aredisclosed and. claimed in my copending application Serial #137,667 filedApril 19, 1937, and in my copending application Serial #140,900, led May5, 1937.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is:

l. In a control system, in combination, a fluid pressure conduit, valvemeans having a neutral position and in said conduit to control themagnitude of the pressure in that portion of the conduit beyond saidvalve means, means for displac ing said valve means from the neutralposition .to admit pressure fluid to that portion of said conduit beyondsaid valve means upon departure of a condition to be controlled in onedirection from a predetermined value and for displacing said valve meansfrom the neutral position to discharge pressure iiuid from that portionof said conduit beyond said valve means upon departure of the conditionin opposite direction from the predetermined value,`means for restoringthe valve to the neutral position controlled by the pressure of thefluid within that portion of said conduit beyond said valve means, andmeans controlled by the pressure of the fluid within that portion of theconduit beyond said valve means for preventing the valve from remainingin neutral position until the condition attains a predetermined value.

2. A pressure balancing device comprising in combination, a rst pressurechamber having a flexible wall, an enclosure forming second and thirdpressure chambers separated by a. common flexible wall, a restrictedconnection between said last named chambers, mechanical means connectingthe flexible walls together for simultaneous movement, openings in saidthird named chamber for the admission and discharge of pressure uid fromsaid chamber, and a fulcrumed beam positioned in said third chamberprovided with valve members for governing the admission and discharge ofpressure fluid from said chamber having a neutral position, said beamactuated by said mechanical means to maintain a pressure within saidthird named chamber tending to hold. the fulcrumed beam in the neutralposition.

3. In a control system, in combination, means sensitive to a conditionto be controlled, valve means actuated by said first named means forproducing a first uid pressure in accordance with the magnitude of thecondition, a pressure balancing device comprising a pressure chamberhaving a flexible wall, means for admitting the first fluid pressure tosaid chamber, an enclosure .forming twp pressure chambers separatedby acommon flexible wall, a restricted connection between said last namedchambers, mechanical means connectingthe flexible walls together forsimultaneous movement, means responsive to the movement of said exiblewalls for increasing or decreasing the pressure'in one of said lastnamed chambers tending to hold said exible Walls in a neutral position,and regulating means for an agent producing or maintaining saidcondition controlled by the last named pressure.

d. A'pressure balancing device comprising in combination a rst pressurechamber having a movable Wall. a second pressure chamber having amovable wall, valve means for ladmitting and for discharging pressuresfrom said second pressure chamber, valve members for controlling the ovvof pressure uid through each of said valve means, a fulcrumed beamWithin the second named pressure chamber for actuating said valvemembers in unison, yieldable means normally urging said valve members ina closed direction, means for transmitting movements of said movableWalls to said fulcrumed beam for actuating said valve members, and meansfor urging said fulcrumed beam against said last named means.

5. A pressure balancing device comprising in combination, a pair ofopposed pressure chambers each having a movable wall, valve ports to oneof said chambers for admitting and discharging pressure :duid from saidchamber, movable valve members cooperating with said ports in thecontrol oi the admission and discharge of the pressure duid, a beamfulcrumed between said ports for actuating one or the other of saidvalve members when displaced from the neutral position, resilient meansnormally urging said valve members to a closed position, mechanicalmeans to produce opposing forces on said member, valve ports in one ofsaid chambers for admitting and discharging pressure ud from one of saidchambers, movable valve members cooperating with said ports in thecontrol of the pressure uid, a beam for selectively actuating said valvemembers arranged to be displaced from a. neutral position by saidmovable member, and means for producing a variable force on said movablemember comprising a spring, and hand operable means for varying thetension on said spring.

7. In a control system in combination, means sensitive to a condition tobe controlled, valve means actuated by said ilrst named means'forproducing a uid pressure in` accordance with the magnitude of thecondition, a pressure balancing device comprising a rst pressure chamberhaving a movable Wall, a second pressure chamber having a movable wall,valve means for admitting and for discharging pressures from said secondpressure chamber, valve members for controlling the flow of pressurefluid through each of said valve means, a fulcrumed beam Within thesecond named pressure chamber for selectively actuating said valvemembers, yieldable means normally urging said valve members in a closeddirection, means for transmitting movements of said movable walls tosaid fulcrumed beam for actuating y apodera. i

said valve members, and-means for urging said fulcrumed beam againstsaid last named means.

8. In a control system for maintaining a condition at a predeterminedvalue, in combination, a huid pressure conduit, valve means having a.

neutral position in said conduit for controlling admission to and Wasteof pressure nuid therefrom, means for displacing said valve means fromthe neutral position to admit pressure uid to said conduit upon a'changein magnitude of said condition in one sense, and to Waste rluid pressurefrom said conduit upon a change in magnitude of said condition inopposite sense, means tending Ato restore said valve means to theneutral position controlled by the pressure iluid within said conduit,and means controlled by the pressure of the fluid Within the conduittending to prevent the valve means from remaining in neutral positionuntil the condition attains the predetermined value.

9. In combination, a casing defining a pair oi' chambers separated by apressure sensitive exible partition, a second pair of chambers separatedby a second pressure sensitive flexible partition, means operativelyconnecting said exible partitions; and a supply and waste valvecontrolling a uid pressure in one of said chambers under the control ofsaid last named means.

10. A relay device comprising a member movable to and from a neutralposition, uid pressure supplyand exhaust control means actuated by saidmember, pressure responsive motors acting on said member for impressingforces thereon proportional to the pressures Within said pressureresponsive motors; the rst of said pressure responsive motors beingresponsivevto a variable pressure, the second pressure responsive motorcommunicating with said uid pressure supply and exhaust control means,means responsive to fluid pressure and including a chamber, said meansimpressing a force on said member proportional to the iluid pressurewithin said chamber, a. restricted connection between said chamber andone of the pressure responsive motors for gradually changing thepressure within said chamber in response to the change in pressureWithin one of said pressure responsive motors, the resultant of theforces impressed on said member by said iirst pressure responsive motorand said means acting to move said member from its neutral position,said fluid pressure supply and exhaust control means being operated bysaid movable member to increase or decrease the pressure acting in thesaid second pressure responsive motor so that for each value of theresultant of the forces impressed on said member by said lrst pressureresponsive motor and by said means, the member is moved toward itsneutral position by the force impressed on said member by said secondpressure responsive motor.

11. In a uid pressure operated control system, in combination, a relaydevice comprising a member movable to and from a neutral position, uidpressure supply and exhaust control means actuated by said member,pressure responsive motors acting on said member to impress forcesthereon proportional to the pressures within said pressure responsivemotors; the first of said pressure spaans on said member by the iirstuid pressure motor and said means acting to move said movable memberfrom its neutral position, the second of said pressure responsive motorsin communication with the fluid pressure supply and exhaust controlmeans and impressing on said member a force acting in opposition to theresultant of the forces impressed on said member by the rst pressureresponsive motor and said means, said uid pressure supply and exhaustcontrol means operated by said movable member to increase or decreasethe pressure acting in the second pressure responsive motor so that foreach value of the resultant of the forces impressed on said member bythe first pressure responsive motor and said means, the member is movedtoward its neutral position by the force impressed on said member bysaid second pressure responsive motor, a restricted passage between saidchamber and one of the pressure responsive motors whereby an initialchange in the pressure within the second pressure responsive motor dueto a change in the pressure within the rst pressure responsive motor isfollowed by a further change in the pressure within the second pressureresponsive motor due to the change in pressure within said chamber and auid pressure servomotor responsive to the pressure within the secondpressureresponsive motor for regulating the rate of application of anagent aiecting the condition.

HARVARD H. GORRIE.

